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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.execution__connect"></a><a class="link" href="execution__connect.html" title="execution::connect">execution::connect</a>
</h3></div></div></div>
<p>
        <a class="indexterm" name="boost_asio.indexterm.execution__connect"></a>
      </p>
<p>
        A customisation point that connects a sender to a receiver.
      </p>
<pre class="programlisting"><span class="keyword">constexpr</span> <span class="identifier">unspecified</span> <span class="identifier">connect</span> <span class="special">=</span> <span class="identifier">unspecified</span><span class="special">;</span>
</pre>
<p>
        The name <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">connect</span></code> denotes a customisation point object.
        For some subexpressions <code class="computeroutput"><span class="identifier">s</span></code>
        and <code class="computeroutput"><span class="identifier">r</span></code>, let <code class="computeroutput"><span class="identifier">S</span></code> be a type such that <code class="computeroutput"><span class="keyword">decltype</span><span class="special">((</span><span class="identifier">s</span><span class="special">))</span></code>
        is <code class="computeroutput"><span class="identifier">S</span></code> and let <code class="computeroutput"><span class="identifier">R</span></code> be a type such that <code class="computeroutput"><span class="keyword">decltype</span><span class="special">((</span><span class="identifier">r</span><span class="special">))</span></code>
        is <code class="computeroutput"><span class="identifier">R</span></code>. The expression <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">connect</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">r</span><span class="special">)</span></code> is expression-equivalent to:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span class="identifier">connect</span><span class="special">(</span><span class="identifier">r</span><span class="special">)</span></code>,
            if that expression is valid, if its type satisfies <code class="computeroutput"><span class="identifier">operation_state</span></code>,
            and if <code class="computeroutput"><span class="identifier">S</span></code> satisfies <code class="computeroutput"><span class="identifier">sender</span></code>.
          </li>
<li class="listitem">
            Otherwise, <code class="computeroutput"><span class="identifier">connect</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">r</span><span class="special">)</span></code>,
            if that expression is valid, if its type satisfies <code class="computeroutput"><span class="identifier">operation_state</span></code>,
            and if <code class="computeroutput"><span class="identifier">S</span></code> satisfies <code class="computeroutput"><span class="identifier">sender</span></code>, with overload resolution performed
            in a context that includes the declaration <code class="computeroutput"><span class="keyword">void</span>
            <span class="identifier">connect</span><span class="special">();</span></code>
            and that does not include a declaration of <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">connect</span></code>.
          </li>
<li class="listitem">
<p class="simpara">
            Otherwise, <code class="computeroutput"><span class="identifier">as_operation</span><span class="special">{</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">r</span><span class="special">}</span></code>, if <code class="computeroutput"><span class="identifier">r</span></code>
            is not an instance of <code class="computeroutput"><span class="identifier">as_receiver</span><span class="special">&lt;</span><span class="identifier">F</span><span class="special">,</span> <span class="identifier">S</span><span class="special">&gt;</span></code> for some type <code class="computeroutput"><span class="identifier">F</span></code>,
            and if <code class="computeroutput"><span class="identifier">receiver_of</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;</span> <span class="special">&amp;&amp;</span> <span class="identifier">executor_of</span><span class="special">&lt;</span><span class="identifier">remove_cvref_t</span><span class="special">&lt;</span><span class="identifier">S</span><span class="special">&gt;,</span> <span class="identifier">as_invocable</span><span class="special">&lt;</span><span class="identifier">remove_cvref_t</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;,</span> <span class="identifier">S</span><span class="special">&gt;&gt;</span></code> is <code class="computeroutput"><span class="keyword">true</span></code>,
            where <code class="computeroutput"><span class="identifier">as_operation</span></code> is
            an implementation-defined class equivalent to
          </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">S</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span>
 <span class="keyword">struct</span> <span class="identifier">as_operation</span>
 <span class="special">{</span>
   <span class="identifier">remove_cvref_t</span><span class="special">&lt;</span><span class="identifier">S</span><span class="special">&gt;</span> <span class="identifier">e_</span><span class="special">;</span>
   <span class="identifier">remove_cvref_t</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">r_</span><span class="special">;</span>
   <span class="keyword">void</span> <span class="identifier">start</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="keyword">try</span> <span class="special">{</span>
     <span class="identifier">execution</span><span class="special">::</span><span class="identifier">execute</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">e_</span><span class="special">),</span>
         <span class="identifier">as_invocable</span><span class="special">&lt;</span><span class="identifier">remove_cvref_t</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;,</span> <span class="identifier">S</span><span class="special">&gt;{</span><span class="identifier">r_</span><span class="special">});</span>
   <span class="special">}</span> <span class="keyword">catch</span><span class="special">(...)</span> <span class="special">{</span>
     <span class="identifier">execution</span><span class="special">::</span><span class="identifier">set_error</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">r_</span><span class="special">),</span> <span class="identifier">current_exception</span><span class="special">());</span>
   <span class="special">}</span>
 <span class="special">};</span>
</pre>
</li>
</ul></div>
<p>
        and <code class="computeroutput"><span class="identifier">as_invocable</span></code> is a class
        template equivalent to the following:
      </p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span>
 <span class="keyword">struct</span> <span class="identifier">as_invocable</span>
 <span class="special">{</span>
   <span class="identifier">R</span><span class="special">*</span> <span class="identifier">r_</span><span class="special">;</span>
   <span class="keyword">explicit</span> <span class="identifier">as_invocable</span><span class="special">(</span><span class="identifier">R</span><span class="special">&amp;</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span>
     <span class="special">:</span> <span class="identifier">r_</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">addressof</span><span class="special">(</span><span class="identifier">r</span><span class="special">))</span> <span class="special">{}</span>
   <span class="identifier">as_invocable</span><span class="special">(</span><span class="identifier">as_invocable</span> <span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span>
     <span class="special">:</span> <span class="identifier">r_</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exchange</span><span class="special">(</span><span class="identifier">other</span><span class="special">.</span><span class="identifier">r_</span><span class="special">,</span> <span class="keyword">nullptr</span><span class="special">))</span> <span class="special">{}</span>
   <span class="special">~</span><span class="identifier">as_invocable</span><span class="special">()</span> <span class="special">{</span>
     <span class="keyword">if</span><span class="special">(</span><span class="identifier">r_</span><span class="special">)</span>
       <span class="identifier">execution</span><span class="special">::</span><span class="identifier">set_done</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">r_</span><span class="special">));</span>
   <span class="special">}</span>
   <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()()</span> <span class="special">&amp;</span> <span class="keyword">noexcept</span> <span class="keyword">try</span> <span class="special">{</span>
     <span class="identifier">execution</span><span class="special">::</span><span class="identifier">set_value</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">r_</span><span class="special">));</span>
     <span class="identifier">r_</span> <span class="special">=</span> <span class="keyword">nullptr</span><span class="special">;</span>
   <span class="special">}</span> <span class="keyword">catch</span><span class="special">(...)</span> <span class="special">{</span>
     <span class="identifier">execution</span><span class="special">::</span><span class="identifier">set_error</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">r_</span><span class="special">),</span> <span class="identifier">current_exception</span><span class="special">());</span>
     <span class="identifier">r_</span> <span class="special">=</span> <span class="keyword">nullptr</span><span class="special">;</span>
   <span class="special">}</span>
 <span class="special">};</span>
</pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
            Otherwise, <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">connect</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">r</span><span class="special">)</span></code> is ill-formed.
          </li></ul></div>
<h5>
<a name="boost_asio.reference.execution__connect.h0"></a>
        <span class="phrase"><a name="boost_asio.reference.execution__connect.requirements"></a></span><a class="link" href="execution__connect.html#boost_asio.reference.execution__connect.requirements">Requirements</a>
      </h5>
<p>
        <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/execution/connect.hpp</code>
      </p>
<p>
        <span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio/execution.hpp</code>
      </p>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2022 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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